Method of fabricating dental crowns and bridges from gold

ABSTRACT

The invention refers to a fabricating method for one-piece cast dental crowns, with controlled thickness, as well as for dental bridges consisting of crowns and the bridge body. To this end a calibrated wax cylinder is placed on the tooth stump, this cylinder being flared in order to form proximal contact points with the adjoining teeth, thus realizing practically also the control of thickness; over the wax cylinder a lid is applied at the level of the occusal surface and in which the occlusal relief is fashioned in relation to the contact points of the antagonistic teeth. In the case of dental bridges, the patterns of the respective crowns are fashioned first, as above, then the pattern of the bridge body which is united with the pattern of the crowns, after which follows the casting of the entire assembly from a gold alloy.

United States Paten Costa et al.

[ ME-THOD OF FABRICATING DENTAL CROWNS AND BRIDGES FROM GOLD Inventors: Eugene Costa; Lucian Ene; Stelica Dumitrescu; loan Covaci, all of Bucharest, Romania [73] Assignee: Pollclinica de Stomatologie Protetica, Bucharest, Romania 221 Filed: Sept. 23,1970 21 Appl.No.: 74,821

521 U.s.c|.Q ..164/35, l64/DIG.4, 164/45,

I 164/376 51 Int. Cl. ..B22c 9/04,A61c 13/20 [58] Field of Search....l64/34, 35, 45, 235, 249, 376, l64/DIG. 4; 249/54; 32/70 [56] References Cited UNITED STATES PATENTS 1,465,472 8/ 1923 Hansen 164/34 X 2,196,505 4/l940 Morton ..l64/35 X 3,224,050 12/ l 965 Redtenbacher ..249/54 X FOREIGN PATENTS OR APPLICATIONS 508,204 6/1939 Great Britain ..249/54 Primary Examiner-R. Spencer Annear Attorney-Karl F. Ross [57] ABSTRACT The invention refers to a fabricating method for onepiece cast dental crowns, with controlled thickness, as well as for dental bridges consisting of crowns and the bridge body. To this end a calibrated wax cylinder is placed on the tooth stump, this cylinder being flared in order to form proximal contact points with the adjoining teeth, thus realizing practically also the control 9 Claims, 17 Drawing Figures PATENTEDnm |972 SHEET 1 BF 2 FIG. IO

FIG. 9

PATENTE'lmm 3 1912 SHEU 2 [IF 2 F'IG.

FIG. 12

' FIG. 13

FIG. 135

FIG. /3a

FIG. [5

FIG. 14

METHOD OF FABRICATING DENTAL CROWNS AND BRIDGES FROM GOLD l. FIELDOF THE INVENTION bridges using crowns which form the constituting ele- I ments, as in the case of gold bridges.

2. BACKGROUND OF THE INVENTION There are known technical methods for the fabrication of gold crowns cast with controlled thickness, or with uncontrolled thickness.

The known fabricating methods with uncontrolled thickness present the following drawbacks:

they need much precious metal such as gold and platinate gold;

the patterns fashioned with conventional wax and applied by, dripping or by immersion are thick and subject to contraction and dimensional modification because of the internal stresses which are formedduring manufacture; I r v the crowns after. casting are highly susceptible to contraction, the investmentmaterials unable to compensate for the contraction coefficient of l.3-l .8 and therefore, need prolonged subsequent processing, the latter leads to faulty'crowns, and the consumption of a great quantity of precious metal;

the metal, separated from the tooth by only a thin cement film, transmits temperature variations which result ultimately in the injury of the dental pulp;

removal of the crowns, is very difficult on account of the thickness of the crowns, and much time and precious metal are lost.

There are also known methods for the control of the thickness of the crown, in order to made it thinner, creating a space between the walls of the crown and of the tooth stump, destined to solve all the inconveniences mentioned, these methods including the use of lead sheet, the covering of the plaster stump with investment material, the thinning of the crown by means of a thread and modeling or sculpting.

{been abandoned, and intheir stead other methods for the fabricating of cast gold crowns have been developed which, however, required the duplication of the models, which is a time-consuming and complicated technique.

There exists also another method using gold crowns consisting of two parts, a ring and a cast lid.

These crowns have solved partially the drawbacks mentioned, but they have the disadvantage that the adaptation of the ring on the polished stump in the buccal cavity is not accurate. Besides, modifications occur, namely internal tensions, in the structure of the gold alloy, favored by the heatingof the ring and of the cast lid when they are united by soldering.

3. SUMMARY OF THE INVENTION The method, according to the invention, eliminates the above-mentioned disadvantages by that using, in

0 the case of the fabrication of individual dental crowns,

a cylinder of calibrated wax (wax of given thickness) applied over the tooth-stump on the working model, over which wax cylinder is applied a lid of the same calibrated wax and on which the occlusal relief is fashioned, using dripped wax, in order to reproduce the occlusal relief with the contact points in a correct relation to the antagonistic teeth; one-piece cast bridges are realized by uniting the pattern of the bridge body with the pattern of the dental crowns which form the constituting elements, this operation being followed by the casting of the gold alloy after the investment casting of the pattern so formed.

4. DESCRIPTION OF THE DRAWING In the drawing:

FIG. 1 is a longitudinal section through the complex model with the impression obtained with a ring and thermoplastic material of the hard plaster tooth-stump fastened to a plastic support;

FIG. 2 is a longitudinal section through the complex model, after the removal of the ring and of the thermoplastic material;

FIG. 3 is a longitudinal section of the complex model, comprising the calibrated wax cylinder applied on the crown stump and flared, in order to realize points of contact with the adjoining teeth and control of thickness;

FIG. 4 is a longitudinal section through the complex model, on the calibrated wax cylinder being applied a lid that will reproduce the occlusal relief;

FIG. 5 is a longitudinal section through the crownstump and the plastic support, on which one can crown-stump the calibrated wax cylinder reproducing the occlusal relief;

FIG. 6 is a longitudinal section through the complex model and the wax pattern, after final fashioning, on which are applied the casting canals (sprue) andthe pressure canal (vent);

FIG. 7 is a longitudinal section through the complex FIG. 11 is a longitudinal section of the hard plaster model to which is applied the flared calibrated wax cylinder in order to realize contact points and to control thickness;

FIG. 12 is a longitudinal section of the hard plaster model to each calibrated wax cylinders of which is applied a wax lid that will reproduce the occlusal relief, the pattern of the bridge body being united, ultimately, with the pattern of the crowns;

FIG. 13 is three longitudinal sections of the hard plaster model and the wax pattern (a, bridge b,c, crowns), after final fashioning, on which are applied the casting canals and the pressure canals;

FIG. 14 is a longitudinal section through the hard plaster model and through the pattern provided with the casting funnel, the investment material being uniformly distributed on the pattern left on the model; and

FIG. is a longitudinal section through the invested pattern complex and through the cylindrical former with which the mold for casting is obtained.

5. SPECIFIC DESCRIPTION Example I (FIGS. 1-8) For the execution of dental crowns cast from gold, with controlled thickness, the impression of the stump is taken in the dental office under conditions known in themselves. Over this impression containing the ring or the rings and having in the interior thermoplastic material, the impression is taken with plaster.

Into the crown-stump impression obtained with a copper ring and thermoplastic material hard plaster is poured, after which a support made of plastic is fixed in the impression. After the final setting, of the hard plaster, the ring with the thermoplastic material, together with the plastic support is placed exactly into the plaster super-impression, which is subsequently, entirely reconstituted. Into the super-impression, isolated with water and soap, conventional plaster is poured in order to obtain the extended model of the semi-arch and of the antagonistic teeth. After the removal of the impression, an aggregate model 1 of conventional plaster is obtained, in which slides a plastic support 2 with the mobile crown-stump 3 covered with a copper ring 4 and thermoplastic material 5.

The ring with the thermoplastic material is removed from the mobile stump 3 of the working model 1, which permits the starting of the fashioning of the pattern.

The fashioning of the crown pattern begins with the first phase which consists in the application of a calibrated wax band of 0.3-0.4 mm which will surround the stump 3, having the shape of a wax cylinder 6, starting from the collet area and reaching up to the occlusal area of the tooth.

In order to obtain the space between the walls of the crown and of the stump, which constitutes, practically, the control of thickness, the wax cylinder 6 is given a flared shape by means of a fashioning tool, until the realization of the contact points 7 with the adjoining teeth, aiming, at the same time, to obtain an anatomical shape of the future crown.

If the height of the stump 3 is very small and if there exists a very large space between this tooth-stump 3 and the contactpoints with the antagonistic teeth, the wax cylinder 6 will be longer and will exceed the occlusal surface of the stump 3 to near the contact surface with the antagonistic teeth.

For the fashioning of the occlusal surface the same calibrated wax of 0.3-0.4 mm thickness is used in the first phase. On the occlusal surface, of the stump 3, a wax lid 8 is applied subsequently, which lid is attached to the wax cylinder 6, by being pressed gently by means of a rubber instrument, in order to bring about an intimate contact only with the occlusal face of the stump 3. In order to avoid the danger of plugging, in case the tooth-stump is too short, a plug (not represented in the drawing) is applied in the crown pattern, which plug is located between the occlusal surface of the stump 3 and the wax lid 8.

The second phase consists in the completion of the fashioning of the pattern to which end the occlusal face 9 is completed with wax added dropwise, which results in the modelling of the occlusal relief in a correct relation to the antagonistic teeth. Since the physician touches up, as a rule, the crowns at the contact points with the adjoining or antagonistic teeth,'it is recommended to thicken the pattern at these levels by means of small drops of wax 10 applied on the external face of the pattern. A pattern 11 is finally obtained, with a controlled thickness, of the isolated crowns. The pattern left on the working model 1 is prepared for being invested into a special investment material for precious alloys. Levelling and depreasing is carried out by the following technique: a little cotton-wool is wrapped round a small stick which is soaked with eucalyptus oil, oiling with it a small area of the pattern 11.

Before proceeding to another portion, the oiled portion is brushed with acetone. The eucalyptus oil dissolves slowly the wax, making it smooth. Acetone stops this action, dries and degreases the pattern 1 1 realizing smooth surfaces. Under such working conditions the modelling of the pattern will be reproduced exactly and the cast pieces will require no costly and time-consuming processing.

Subsequently, on the oral occlusal margin, at the thickest point of pattern 11, are applied the casting canals 12 with diameters of about 1.5 mm, which are united at a point, 12 a.

At 2-3 mm from the pattern 11, on the casting canals l2 contraction balls 13 are then placed, these balls having diameters of about 4 mm and having the role of transforming the construction into a tank which will feed the filling of the mould with melted gold. Also, the tanks incorporate into the construction pores that cannot be avoided and which, as a fact, will not be detrimental to the cast piece in any way.

On the vestibular cervical margin of the pattern 1 1, a round wax profile or a 0.8 mm diameter nylon thread is applied, which will become the air evacuation canal 14 after burning.

This canal 14 will enable the evacuation of the compressed air which forms within the mold at the moment of the penetration of the molten material. I

The pattern 11, together with the casting canals 12, is fastened to a former of the casting funnel 15, into the hole located at the most conical part 16 of the former and is attached to this with heated wax.

The round wax profile 14 of the pressure evacuation canal is attached to the casting funnel outside the zone of penetration of the molten metal 17. Then the investment casting of the pattern 11 is carried out on the working model 1, after it has previously been isolated by introducing it into water. The first layer of investment material 18 is distributed uniformly and with a sufficient thickness on the occlusal, vestibular, and oral surfaces of pattern 11.

After the setting of this first layer of investment material 18, the half-invested pattern 11 is removed from the working model 1, thus avoiding the risk of deformation. The investment of the internal part of the crown is further continued, completing the whole cupshaped pattern 11. The pattern complex 11, the casting canals 12, the air evacuation canals l4 and the casting funnel 15 are introduced into a cylindrical former 19 of plastic, into which has been poured the same investment material 18, suitable for precious metals, or a mixture of plaster, sand and water. The final setting of the investment material 18, used for the realization of the mold, as well as the removal of the cylinder 19 and of the former of the casting funnel l5, constitute the final stage, obtention of the mold.

The mold is then introduced into the furnace in order to allow the wax to trickle down and dry. The temperature is raised gradually, so as to attain, after one hour, 750-800 C. The'temperature at which thermal dilatation occurs is maintained-without exceeding it for half-an-hour, the time needed for a complete burning of the carbon resulting from the melting of the wax.

The mold is removed from the 'furnace after having prepared previously the casting centrifuge. The flame is adjusted in order to bring about a rapid melting and fluid state of the wax. In order to achievethis, the casting funnel must not be deep, avoiding in this way a nonuniform heating or an over-heating of the alloy, with all the consequences resulting from non-homogenization and oxidation. After casting, the mold is left to cool slowly for 5-8 minutes, after which it is immersed in water.

Correct pickling is carried out in a 10 percent solution sulphuric acid, which is heated together with the prosthetic piece introduced into a bucket, until a temperature of about 60C is reached. After pickling, the sulphuric acid is poured into another vessel and the prosthetic piece is washed with water. The processing and finishing of the cast crown, with controlled thickness, are effected by techniques known in themselves. The close observance of the technology of this example, according to the invention, enables the realization of accurate and homogeneous prosthetic pieces, that will require no time-consuming processing, which would result in great losses of precious metal.

Example 2 (FIGS. 9-l5) In the case of one-piece cast dental bridges, the realization of dental crowns forming the anchors is identical with that used in the case of the fabrication of isolated dental crowns, the pattern of the bridge body being united with the pattern of the crowns.

For the execution of the bridges, the impression'of the stumps is obtained correctly by means of a copper ring and thermoplastic material, over which a super-impression is taken with plaster.

In the case of one-piece cast bridges it is recommened to cast the model without mobile crown-stumps 20 in order to avoid any error regarding the position thereof. The removal of the rings 4 with the thermoplastic material 5 from the working model 1 permits modelling of the pattern. For the realization of the pattern, in the case of crowns, the same calibrated wax of 0.3-0.4 mm thickness is used, this wax being applied I the collet up to the occlusal area of the tooth. The same calibrated wax band is applied in the form of a wax cylinder 6, on all the teeth that will form the constituting elements. The space between the walls of the crowns and of the stumps 20 is realized by the flaring of the wax cylinder 6, aiming as shown in FIG. 2 at the same time to realize contact points at 7 and to reproduce the anatomical shape of the future crown. The wax lid 8 is applied over the occlusal surface of the stumps 20 and is attached to the wax cylinder 6. By completing with dripped wax 10 the occlusal surface, the fashioning of the occlusal relief 9 is obtained in a correct relation to the antagonistic teeth, not represented in the drawing.

Just as in the case of isolated dental crowns 11, the pattern of the crowns 21 will be thickened at the contact points with the adjoining and antagonistic teeth by means of small wax drops applied on the external face of pattern 11.

The further fashioning of the bridge body 20 will be carried outaccording to a technique known in itself in the case of a massive bridge body, while the modelling of the casettes is carried out by hollowing-out in order to avoid certain complications (the trickling of the wax over the pattern of the crowns); the pattern of the bridge body 22 is united with the pattern of the crowns 21 by means of dripped wax.

The final control considers the fashioning of the pattern as finished; the smoothing and degreasing of the pattern is done as in the case of isolated crowns. Subsequently, on each crown pattern 21 a metal-casting canal 12 is applied on the occluso-oral margin and, depending on the length of the bridge body, one or several rods.

On the vestibular cervical edge of the pattern, a round wax profile 14 or a 0.8 mm diameter nylon thread is placed. This canal will permit the evacuation of the compressed air, which forms within the mold, at the moment of the penetration of the molten metal.

The pattern together with the casting canals l2 and with the profiles 14 of the evacuation canals is fastened to the former of the casting funnel 17. The investment of the pattern in the case of one-piece cast bridges is executed on the working model 1. After the setting of the investment material 18, the pattern is removed from the working model 1 and the investment of the in ternal part of the crowns is continued, until the completion of all the patterns. The completely invested pattern complex is introduced into a cylindrical former 19 of plastic, into which has been poured the same investment material 18, suitable for precious metals, obtaining the final setting the mold.

For the realization of the mold, one can use also a mixture 1:3 of plaster and sand, and water, which is introduced into the former, followed by the introduction of the invested pattern complex. Heating of the mold, melting of the gold alloy, cooling of the mold after casting, pickling and preocessing are identical with those used in the fabrication of isolated crowns, as has been shown in example 1..

The method, according to the invention, presents the following advantages:

it permits the execution of cast isolated crowns with controlled thickness from precious alloys, with great accuracy and homogeneity, thus replacing the known methods which required on the part of the dental technician great dexterity at the moment of the removal from within the pattern of the materials by means of which thickness has been controlled;

dental bridges can be fabricated from one piece, the crowns with controlled thickness and the bridge body,-replacing thus the technique of soldering, known in itself, after casting of the crowns with the separately cast bridge body;

it eliminates the trial of the crowns forming the constituting elements of the bridges, trial which was absolutely necessary in the techniques up to now, eliminating for the patient and the physician the sessions necessary as yet for this phase and thus speeding up the execution of the works;

it enables the saving of precious metal (for instance, for a molar crown of usual size, with non-controlled thickness, 3.50 g of gold are consumed, on the average, while for the same crown of usual size executed according to the present method 2.20 g of gold are consumed on the average);

the cast prosthetic pieces are homogeneous and of adequate resistance (free of internal tensions), since they are not subjected to successive heatings as in the case of dental crowns with ring and cast lid which are united by soldering with the separately cast bridge body.

What we claim is: l. A method making a dental prosthesis, such as a dental bridge or crown, comprising the steps of: forming a positive model of a tooth stump; applying over said model a substantially cylindrical and hollow body of wax of substantially uniform wall thickness; applying to one end of said body and over the occlusal surface of said model a wax disk having substantially the same thickness as said body, thereby forming a wax cup of substantially uniform wall thickness partially receiving said model;

contouring the exterior of said cup by addition of additional wax to impart the desired tooth shape to said cup; and

investment casting a dental crown from the contoured cup.

2. The method defined in claim 1, further comprising the step of flaring said cylindrical body to form an empty space between it and said model.

3. The method defined in claim 2 wherein the flaring step is carried out prior to the application of said disk to said cylinder.

4. The method defined in claim 3 wherein said positive model is formed of plaster.

5. The method defined in claim 3 wherein said cylindrical body is made of acalibrated band of wax.

6. The method defined in claim 3 wherein said cylindrical body and said disk have a thickness between 0.3 and 0.4 millimeters.

7. The method defined in claim 3 wherein said positive model is formed of a mouth region having a pair of tooth stumps to be interconnected by a dental bridge, a contoured cup being fashioned for each of said stumps, said method further comprising the step of forming between said cups a wax bridge having a shape corresponding to the desired bridge sha pe, both of said cups and said wax bridge being simul aneously investment cast in metal.

8. The method defined in claim 7 wherein said cups and bridge are cast of an alloy containing gold.

9. The method defined in claim 7 wherein both of said cups are formed the respective tooth-stump models and said bridge is formed between said cups while they are mounted on their respective tooth-stump models. 

1. A method making a dental prosthesis, such as a dental bridge or crown, comprising the steps of: forming a positive model of a tooth stump; applying over said model a substantially cylindrical and hollow body of wax of substantially uniform wall thickness; applying to one end of said body and over the occlusal surface of said model a wax disk having substantially the same thickness as said body, thereby forming a wax cup of substantially uniform wall thickness partially receiving said model; contouring the exterior of said cup by addition of additional wax to impart the desired tooth shape to said cup; and investment casting a dental crown from the contoured cup.
 2. The method defined in claim 1, further comprising the step of flaring said cylindrical body to form an empty space between it and said model.
 3. The method defined in claim 2 wherein the flaring step is carried out prior to the application of said disk to said cylinder.
 4. The method defined in claim 3 wherein said positive model is formed of plaster.
 5. The method defined in claim 3 wherein said cylindrical body is made of a calibrated band of wax.
 6. The method defined in claim 3 wherein said cylindrical body and said disk have a thickness between 0.3 and 0.4 millimeters.
 7. The method defined in claim 3 wherein said positive model is formed of a mouth region having a pair of tooth stumps to be interconnected by a dental bridge, a contoured cup being fashioned for each of said stumps, said method further comprising the step of forming between said cups a wax bridge having a shape corresponding to the desired brIdge shape, both of said cups and said wax bridge being simultaneously investment cast in metal.
 8. The method defined in claim 7 wherein said cups and bridge are cast of an alloy containing gold.
 9. The method defined in claim 7 wherein both of said cups are formed the respective tooth-stump models and said bridge is formed between said cups while they are mounted on their respective tooth-stump models. 